Venezuelan authorities on Monday released a dozen demonstrators who had been arrested over the weekend while protesting swelling lines at supermarkets, following several days of scattered unrest that included a group of masked assailants burning a bus.

Alfredo Romero, head of rights group Penal Forum said via his Twitter account that 12 protesters were set free on condition that they appear in court every 30 days.

Venezuela, mired in a recession and with the highest inflation rate in the Americas, is suffering from chronic shortages of goods ranging from diapers to flour that have worsened this year due to an ebb in deliveries during Christmas.

The scarcity of goods has forced many shoppers across the OPEC nation to queue up in front of supermarkets before dawn. The inflation rate hit 63.6 percent in the 12 months to November.

The MUD accused National Guard troops posted to maintain order outside shops of banning photos and videos of the lines that sometimes snake around blocks.

“Not only is the government forcing people to get into humiliating queues... it also wants the lines to be 'Cuban-style,' silent and terrified,” said MUD chief Jesus Torrealba.

On Saturday, an explosive device was thrown into a building of state phone company Cantv in the southeastern city of Puerto Ordaz, burning eight vehicles, the government said. In western San Cristobal, a bus belonging to a local university was burned in the early hours of Monday, witnesses said.

While the scattered protests are a far cry from massive demonstrations that rocked the country for four months in 2014, they come amid growing frustration over the economic crisis.

President Nicolas Maduro, who has seen his popularity plunge, says right-wing agitators and Venezuela's wealthy elite are trying to topple him via an “economic war.”

“At the start of this year the parasitical oligarchy ambushed us but we and the people are responding,” he said at the weekend from Saudi Arabia.

In the last week Maduro and his closest ministers have visited China, Russia and fellow OPEC members to seek financing and OPEC action on tumbling oil prices.

Critics blame Venezuela's recession on socialist policies such as a 12-year-old exchange control system which struggles to provide enough hard currency for imports.

State-run supermarkets have started restricting access based on identity cards. Only Venezuelans whose card number ends in 0 or 1 were allowed to shop on Monday, local media reported.

Officials in Caracas have blamed “media hype” and “panic buying” for the chaotic scenes at outlets around the nation. One state governor has banned queues at night.